It would be nice if games didn't maliciously try to put hooks into players at every turn. But you can learn to balance it.
I have a Dojo with just my group of friends. We build it out with just what we need to progress. We play for like a month every few years, when the itch hits.
I doubt there's a lot there.
It sounds like they got pretty far into exploring what they might make, and how much it would take, but decided not to commit because they didn't want to do something half-assed, and going full-tilt on yet more of the same was beginning to feel like squeezing water from a stone.
They might have something playable, and a lot of the plot worked out, but have almost none of that plot be playble.
Asking them to just "throw things together into a DLC real quick" ignores the fact that the final 10% of getting a project done takes 90% of the effort.